The major objectives of this project are: (1) to study the effects of immunosuppression on the pathogenesis of experimental viral infections, particularly those which have the ability to involve the central nervous system (CNS), (2) to use the immunosuppressed virus-infected animal as a recipient of adoptively transferred lymphoid cells or serum from syngeneic virus immune donors in an attempt to assess the relative contributions of the cellular and humoral immune responses to the outcome of infection, and (3) to correlate these in vivo observations with functional immuno-specific activities which can be measured more quantitatively in vitro by using purified lymphocyte subpopulations or defined antibody classes. Currently under study are several arboviruses which produce a direct cytolytic effect on susceptible neuronal elements and lymphocytic choriomeningitis virus, a noncytopathic agent which produces immune-mediated CNS disease. BIBLIOGRAPHIC REFERENCES: Nathanson, N., Johnson, E.D., Camenga, D.L., & Cole, G.A. Immunosuppression and experimental viral infection: the dual role of the immune response. In: The Immune System and Infectious Diseases. 4th Int. Convoc., Immunol., Buffalo, N.Y., 1974, ed. by E. Neter and F. Milgrom, S. Karger, Basel, 1975, pp. 76-94. Johnson, E.D., & Cole, G.A. Functional heterogeneity of lymphocytic choriomeningitis virus-specific T lymphocytes. l. Identification of effector and memory subsets. J. Exp. Med. 141:866-881, 1975.